SPIRIFER 319 



seem to represent the same species. The specimens from both these 

 horizons seem to be more uniformly elongate along the hinge-line, and 

 none of those observed attain so large a size as is common among the 

 examples from the oolite. 

 Horizon . Kinderhook. 



SPIRIFER MISSOURIENSIS Swallow 

 Plate XXXIX, Figs. 11-23 



1860. Spirifer Missouriensis Swallow, Trans. St. Louis Acad. Sci., vol. 1, 

 p. 643. 



Description. Shell of medium size or smaller, wider than long, the 

 greatest width along the hinge-line, cardinal extremities -angular, the pli- 

 cations of the fold and sinus similar to those of the lateral slopes. The 

 dimensions of two individuals are : length of pedicle valve 22.5 mm. and 

 21 mm., length of brachial valve 18 mm. and 17 mm., width 38 mm. and 

 31 mm., thickness 18 mm. and 14 mm., height of cardinal area 3.5 mm. 

 and 3.2 mm. 



Pedicle valve more or less strongly convex, the greatest convexity pos- 

 terior to the middle, the surface curving more or less abruptly from the 

 umbonal region to the cardinal margin on each side of the beak, more 

 gently to the antero-lateral margins, compressed towards the cardinal ex- 

 tremities; beak small, pointed, incurved; cardinal area of moderate 

 height, arched, the curvature increasing towards the beak, lateral mar- 

 gins sharply defined, sloping from the beak to the cardinal extremities; 

 lateral slopes convex towards the center of the valve, more or less com- 

 pressed towards the cardinal extremities, each marked by from 18 to 20 

 subangular plications along the antero-lateral margin which originate 

 from 10 to 13 plications starting at the beak or along the cardinal mar- 

 gin ; from 3 to 5 of the original plications on each side of the beak divide 

 into 2 or 3 in, or a little in front of, the umbonal region and con- 

 tinue in more or less distinct fascicles to the anterior margin, the fur- 

 rows between these groups of plications being stronger and deeper than 

 those between the members of the group ; mesial sinus sharply defined at 

 the beak, becoming less well defined anteriorly, it is subangular or 

 rounded in the bottom, of moderate depth and sometimes somewhat pro- 

 duced anteriorly into a nasute or lingual extension, it is marked by a 

 median plication which originates near the beak and bifurcates in passing 

 to the anterior margin ; on each side there are from 3 to 5 plications which 

 originate from the inner margins of the lateral bounding plications or 

 through the bifurcation of such plications. 



Brachial valve equally or a little less convex than the pedicle, the great- 

 est convexity usually near the middle; mesial sinus sharply defined to- 

 wards the beak by a pair of deeper and stronger furrows than those be- 

 tween the other plications, becoming somewhat less sharply defined ante- 



